Conventional radio telephone systems such as cellular systems use cell-sites having co-located transmitters and receivers to cover geographical regions referred to as cells. Several cell-sites disposed within a particular geographic area are coupled to a master controller called a mobile telephone switching office (MTSO). The MTSO controls the cell-sites and provides an interface connection to the public switched telephone network (PSTN).
Each conventional cell-site uses pre-assigned channel sets to communicate with mobile units in a service area covered by the cell-site. Each channel set typically includes a pair of carrier frequencies with each carrier frequency being used for respective up-link or down-link communications with a mobile unit. Neighboring cell-sites use different channel sets to avoid interference on the same channel and adjacent channels between adjacent service areas.
Conventional cellular systems provide mobility to a subscriber through a procedure referred to as hand-off. According to this procedure, geographically adjacent cell-sites are considered to be neighbor cell-sites. A neighbor cell-site is the cell-site to which a call can be transferred as a mobile unit traverses a current cell-site boundary. A data table called a neighbor list specifies the cell-sites that can receive a hand-off from a particular cell-site. In addition, to increase the simultaneous communication capacity of a system, channel reuse is employed where two sufficiently distant base stations simultaneously use the same channel.
The channel sets and neighbor lists assigned to particular cell-sites as well as cell-site transmission powers are examples of system organization parameters that define the operating characteristics of the system. Such parameters are typically determined using propagation models prior to installation of a system. After installation, the system coverage area produced by the determined parameter settings is verified by field testing. During a typical field test, a mobile test unit is moved throughout the service area while the base stations and test unit transmit respective test frequencies. As the test unit is moved from one sampling location to the next, the respective signal strength of the test frequencies and the corresponding geographic location is detected at the respective base stations and test unit to verify that the system can provide service to the intended coverage area.
Typical wireless communication systems do not have the capability to automatically identify and adapt parameter settings to such changes. Environmental changes that often require parameters setting adjustments include the construction of structures in the coverage area, such as a building in an outdoor cellular system or added walls in an indoor system, or the installation of another wireless communication system in close proximity to the current system. Such changes could degrade system performance and often require an installer to perform computer modeling of the coverage area again to determine the proper parameters settings.
A method that possesses the limited ability of determining frequency channels used by respective cell-sites is described in M. Almgren et al., “Adaptive Channel Allocation in TACS”, IEEE Global Telecommunication Conference Record, pp. 1517-1521 (1995), which is incorporated by reference herein. According to this method, each cell-site monitors received signal strength (RSS) on respective sets of channels over time and uses the channels for establishing communications that have the lowest interference.
Also, some time division multiple access (TDMA) systems, such as those adhering to the Telecommunication Industry Association Interim Standard 136 (TIA IS-136 standard), have the limited ability to dynamically allocate channels during operation of the systems to achieve greater spectral efficiency and communication capacity. In such systems, a cell-site can request an idle mobile unit to measure the RSS or bit error rate of different communication channels and transmit the measurement information back to the cell-site. Such RSS or bit error rate information indicates the interference on the respective channels. Communication can then be established with the mobile unit using the channel with the lowest interference. However, such a dynamic allocation technique is limited to channel allocation for the respective mobile unit that provides the RSS information.
Thus, a need exists for a radio telephone system having enhanced spectral efficiency that employs a substantially automated determination of system organization parameters and that is capable of adjusting for environmental changes.